Microfaunal soil food webs in Mediterranean semi-arid agroecosystems. Does organic management improve soil health?

Soil food webs, which are responsible for relevant ecological functions in agroecosystems such as nutrient cycling and pest and disease suppression, represent a crucial aspect of agricultural sustainability. We studied soil properties and microfaunal food web diversity and functioning in six paired organic and conventional fields located in Central Spain to assess the effects of organic farming on soil diversity and functioning in semi-arid conditions. We hypothesized that organic farming may enhance functioning of soil food webs. Our results showed larger differences between crop types, namely olive groves and vineyards, than between farming scheme, i.e. organic and conventional fields, and few benefits of organic farming in terms of soil fertility. Soil properties (total N, C, and P, available P and K, electrical conductivity, NH4+, NO3-, soil moisture, pH) tended to present higher values in vineyards than in olive groves and in conventional than in organic fields. Some plant-parasitic nematodes were associated to organic fields, especially in vineyards, and all soils fell within a degraded soil food web condition, with low Structure and Enrichment Index values. Nematode metabolic footprints showed relevant seasonal dynamics, with the more intensive herbivore activity in spring. We conclude that the lack of conventional pesticides and mineral fertilizers is probably not enough to improve soil conservation in semi-arid Mediterranean agroecosystems, and thus active soil conservation practices, as reduced tillage or cover cropping, are required to increase agroecosystem sustainability.